Experimental investigation of biogas production from cytrus waste: Co-digestion with cattle manure

Biogas production through anaerobic co-digestion of a mixture of cattle manure and citrus waste using an experimental facility for testing the biochemical methane potential (BMP) was investigated. No buffer solution is added to the mixture in order to use the buffer capacity from cattle manure. Regular measurements of pH, alkalinity, chemical oxygen demand, methane and biogas net production were performed. Three substrate inoculum ratios (SIR) 1:1, 2:1 and 3:1 (g COD/g VSS) were evaluated. Maximum COD removals of 56.4 %, 51.3 % and 48.0 % for the SIRs 1:1, 2:1 and 3:1 were obtained. For all SIR, pH was on the range of 6.5 to 7.5, while the maximum VFA concentration was 4250 mg CH₃COOH l^-1. Alkalinity ranged between 2250 to 4500 mg CaCO₃ l^-1. Both maximum methane production rate (MMPR) and percentage of anaerobic biodegradability were established. BMP of 94.3 to 146.6 mL_STP-CH4/gVSS were calculated for the ratios 1:1 and 3:1, respectively. The highest feasibility for biogas production and methane was established for SIR 3:1.